Continuous flow micro reaction technology is very promising technology, as it offers, as compared to the traditional batch system, a very uniform residence time, much better thermal control, and a lower hold-up, leading to a significant step change in terms of chemical yield and selectivity, and safety.
Continuous flow microreactors are now widely used in labs for testing and developing new routes of synthesis. For laboratory and development work, they offer a very small hold-up with a sufficient residence time, leading to a very small use of material for testing, which is of particular interest in the development phase, shortening the time required to make a requested quantity, and when the raw material is expensive. In addition, the small amount of material involved reduces safety and environmental risks significantly.
The typical throughput of these devices ranges from less than one milliliter per minute to a few dozens of milliliters per minute.
These devices are usually formed in glass or in plastic (e.g. PDMS), which allows visually observation of the advancement of the reaction, and makes them cheap (in some cases even disposable), and easily reconfigurable.
Once a new process has been established, the challenge is to scale for mass production, with much larger throughput (up to several thousands of milliliters per minute). In addition, the properties of the reactor in terms of heat transfer, mixing, residence time distribution, and with a lower or at least the same pressure drop should be maintained.
Entering into mass production thus typically requires using several units in parallel to cope with the total quantity of product required.
The complete duplication of one reactor line, with all its related equipment (feeding pumps, control loops, sensing, supervisory personnel, and so forth) would typically be the easiest way to place several units in parallel, and is often known as “numbering up.”
However, “numbering up” can result in systems that are too complex, too maintenance-hungry, and/or too expensive to operate.